What is crosstalk in Spanish?
Example; when they are in a meeting and one person is making nonsense someone interrupts that person to let him know that is not part of the meeting
In English "cross-talk" at a meeting would be incidental conversation or chatter unrelated to the issues at hand.
The word is borrowed from a radio/telcommunications term that refers to undesired signals or sounds, (voices, static, etc) in a telephone or other communications device that occurs as a result of coupled transmissions or interference.
In Spanish the word for crosstalk is diafonía, but I don't think that it is used in the same sense as in English (incidental conversation) as it is not listed as an entry under "diafonía" in the RAE.
As far as chatter you might use "cháchara" (chit-chat, chatter) or "conversación ociosa" (idle talk), but you might want to wait for a native speaker to clarify whether either of these sounds natural to say.